Production of cellulose derivatives



Patented May 22 1945 2,376,422 PRODUCTION OF OELLULOSE DERIVATIV ES I Henry Dreyfus, London, England No Drawing. Application July 8, 1942, Serial No.

- 450,188. In Great Britain July '15, 1941 9 Claims. (Cl. 260225) This invention is concerned with improvements in the production of cellulose derivatives and particularly withimprovements in the production of mixed esters of cellulose.

According to the present invention mixed esters of cellulose are produced by esterifyinga cellulose ester containing free hydroxy groups attached" either to the nucleus or in a'substituted radicle, particularly celluloseacetate or other lower alifphatic acid ester of cellulose, in a liquid medium comprising the appropriate anhydride and methylene orethylene dichloride or other halogenated hydrocarbon and containing an acidic metal halide as catalyst. The liquid medium employed is one which is a solvent for the catalyst and which, on completion of esterification, yields a liquid medium which is asolvent for themixed ester formed and it is desirable that itshould also be a solvent for the cellulose ester employed as starting material or at least yield a medium which is a solvent for the mixed ester produced at an early stage of the esterification process. If. the

catalyst is not soluble inthe mixture ofhalogenated hydrocarbonand anhydride sufficient acetone'jor other suitable organicliquid may be added to give a medium which is a solvent.

The process, is applicable to the esterification of cellulose esters however they may have been produced. Thus, the esters may be made by suspension, esterification of cellulose with the appropriate anhydride in the presence of a catalyst'and benzene or other non-solvent. The process is,

however, of particular importance in the production of mixed esters from cellulose acetate or other cellulose ester obtained by esterifi-cation. of

cellulose with the acid anhydride in a liquid 'medium which is a solvent for the ester, using 'e. g.

sulphuric acid ascatalyst. i

The present application is particularly concerned with the esterification of lower aliphatic acid esters of cellulose containing free hydroxy groups and more thanl, e. g. 1.5-2.5, acetyl or other acid radicles per CsHioOsnucleus, especially with the esterification .of ordinary-commercial acetone-soluble cellulose acetate, which contains about 2.2-2.4 acetyl groups per CsHmOs nucleus. Other esters of lower aliphatic acids containing less than six carbon atomswhich may be esterified are cellulose formate, propionate, butyrate and glycollate. Cellulose acetates and other esters of varying viscosities, e. g. 10, 20, 50, 100 or more, may be employed as starting materials according to the viscosity required for ,the mixed ester produced. Y

. with similar proportions of acid at temperatures:

, Esterification may be continued until a completely esterified product has been produced or it may be interrupted while the ester still contains a certain proportion of free hydroxy groups, for example 0.3 or 0.1 hydroxy group per CBHIQQ? nucleus. 1

According to the degreeoi esterificationtobe eiTected and the esterification conditions em ployed the reaction may take 2 M3 hours or con siderably more, e. g. or hours. Preferably the reaction is carried out at a moderate temperature, for example at about 45 C. for the first 15-20 minutes, thereafter cooling to, or,

C. It has beenyfound that halogenatedhy: drocarbons, particularly ethylene dichloride, or mixtures of halogenated hydrocarbons, are particularly valuable as the maininert constituent of the esterification medium on account of the good colour of the products obtained when they are employed. Moreover, they are easily recovered from the other constituents of the esterification medium. The liquid medium should be employed in a fairly high proportion based. on the weight. of the ester used, e.,g. 400-600% or more. Ferric and stannic chlorides and particularly zinc chloride are very suitable catalysts, especially when used in conjunction with ahydrohalide acid. They do notthemselves enter into combi:

nation with, the cellulose esterand they do not,

if used in reasonably small proportions, e. g. 05-15% or 2% of the weight of the initial ester,

such, as those mentioned, above, reduce the viscosity ofthematerials unduly. l

The mixed esters with the production of which the present, application is particularly concerned.

are those containing the radicles of two fatty acids, particularly lower fatty acids containing less thansix carbon atomse. g. cellulose aceto propionate, aceto-butyrate and propionate-butyrate. The process is however applicable to the production of, mixedestersin general including; thos containingel g. the stearyl, oleyl or other:

aliphatic acid radicle or the benzoyl or other arc matic acid radicle. The anhydride employed will Y of course depend upon the cellulose ester used as 7 starting material and the mixed ester. which it is desired to produce. played in a proportion of about to or 200% of the quantity theoretically required to produce. the mixed ester desired. This proportion is based on the usual assumptionthat eachfmolecule of anhydride esterifiesone free hydroxy group and forms one molecule of the corresponding acid.

In general, it should be emhot aqueous solution or an organic? acid 'r'ina-iwhich the halogenated hydrocarbon and" the ester are insoluble so as to evaporate off the halogenated V hydrocarbon, thus simultaneously effecting separation of the product, the maininertdiluentand the water-miscible constituents of the esterification solution. Any organic acid present in the aqueous fraction can then be extracted by washing the fraction with the halogenated. hydrocarbon and recovered by fractional distillation of the halogenated hydrocarbon solution. Preferablythe water; or aqueous solution is. used at a temperature slightly above the. boiling pointof the:.halogenated hydrocarbon so: that. the. halo-. genated hydrocarbon is-flashed oiT',,as. it has been found that thisis not-only a convenient method. of separating the halogenated hydrocarbon. but alsothe, physical condition. of the ester is better than it is when precipitation is effected at a lower temperature. It; isLalso desirable, when.

an aqueous solution pf. an organic acid is em-' pIoy'ecL' that the acid should be'the one correspondingw'ith theanhyd'ride employed. 7

'The, following example is given to illustrate the invention,,.ffrom'fwhich.it will be een that in generalit is desirable to employ a low' proportion of catalyst,v a fairly; high proportion of liquid medium, a moderate temperature and a moderate exces'sjof th'e'anhyd'ride.

, w-Eacample "100' parts; of .acetone-soluble cellulose acetate containing about 2.2 acetyl' groups per Gel-I100?) nucleus isintroduced into an esterification medium consisting of about, 600' parts of ethylene dichloride, 60 parts of 88% butyric anhydride', 0.5L part of Zinc chloride, and' 0.25 part of hydrogen chloride, all--by weight The esterification medium'is stirred at a; temperature of" about 45 C.' for IS'minutes and afterwards atabout C; until the requireddeg'ree ofesterification has been effected, which usually takes'a'bout 1cm 24 hours, an'disthen sprayed into'a'large excess of aqueous butyiic' acid of abou't '2-5-% concentration at a temperature of about 90 0;, the temperature of the aqueous medium bei'ng' maintained by the-introduction of. steam'or 'hot" water: The

separated ,from. the (condensate. 'I'heethylene hloride solution. of butyricacid is passedv into a still T andthe constituents ofthe solutionseparate d byfracticnaldistillation.

The precipitated esterlis freed from residual butyrifc acid byjwashing it. or distilling. offjthe' butyrio'acid. with steam. When the purification process is completethe ester may be dried and it is then ready for usefin the production of fila mans on secures industrial articlesg'fl The term fatty acid used in the description and claims is to be understood to refer to formic acid and its higher homologues, i. e. acids having the general formula CnHznOz.

Having described my invention what I desire to secure by Letters Patent is:

1. Process for theproduction of mixed esters of cellulose, which comprises esterifying a carboxylic acid ester of cellulose containing free hydroxy"'groups in a liquidlfn'iedi umicomprising the anhyd'ride of'a different carboxylicacid and a halogenated hydrocarbon, selected from the group consisting of methylene and ethylene dichlorides', andconta-im'ng in solution an acidic metal halide, selected from the group consisting of ferric; starinic and zinc halides, as catalyst in an. amountnot exceeding 2% on the weight of said ester, the liquid medium employed being one i which on completion of esterification yields a' liquid medium which ester-formed.

- 1; 2. Process for: theproductionrofi mixed esters of? cellulose, which comprises esterifying; at carboxylic. acid ester of cellulose containing freev hydroxy groups in, a liquid medium comprising the. anhydride. of. a difierentcarboxylic acid; containing less than six carbon. atoms. and a. halogenated hydrocarbon, selected fromthe. group. consisting. of methylene andethylene dichlorides, .and contain: ing in solution an. acidic metal halide, selected from the groupfconsisting. of ferric, 'stanni'ci zinc halides,- as catalyst in. an..'amount,notfl ex. ceeding 2% on the weight o1 said ester'jthe. liquid medium employed being one. whichon completion of 'esterification yields a liquid medium which is a; solvent for themixed'ester formedl 3'. Process for the. productionofnmixediesters of cellulose, which comprises.esterifying ,a-.fatty acid ester j of cellulose containing free, 'hydr'oxy. groups'in aliquid medium. comprising the an.-

is a solvent for the mixed hydride'of a different fatty acid, and h g n ated hydrocarbon selected from the group Coll. sisting of methylene and'ethylene dichlor'ides. and which contains in solution an acidic metal halide,

selected from the group consisting of ferric, Stan-j me and zinc halides, .asca talyst, in an amount not exceeding 2% of the. weight of said ester, the liquid medium employed'being' onewhich oncompletion of esterification yields a li'q'uid' mediumwhi'chis a solvent for the mixed ester formed? 4; Process for the production of mixed' esters of cellulose, which comprises esterifying' a fatty acid ester of cellulose containing free hydroxy groups in a liquid medium comprising the an: hydride of' a diiferent fatty acid" and a halogen ated hydrocarbon selected from the group con sisting of methylene and ethylene sameness and which contains'insoluti'on an acidic metal c hlo ride, selected from the group'c'onsisting of ferric, stannic and-zinc chlorides; as catalyst, in an amount not exceeding: 2% of the weightofsaid ester,:- the liquid medium employed being one" which on completion ofesterificatiomyiel'ds a liquid medium whichuis a" solvent'fonthe mixed ester' formed.

5.,Process-for the. production-of.'mixed"esters" of. cellul ose,.which comprises esterifying a fattyacid ester of cellulose containing free hydroxy groups. in a liquid -medi-umcomprising the an hydride of ,a difierent fatty acid and a'ha-logerr ated hydrocarbonselected". from theeroup consisting of methylene and ethylene,dichlorides'and which containsa mixture of an acidicimetal ch10.- ride', selected from the group-consisting ofyferrie.

; stannic and zinc chlorides, and hydrochloric acid:

as catalyst, each in an amount not exceeding 2% of the weight of said ester, the liquid medium en'iployed being one which on completion of esterification yields a liquid medium which is a acid ester of cellulose containing free hydroxy groups in a liquid medium which comprises the anhydride of a different fatty acid and an halogenated hydrocarbon selected from the group consisting of methylene and ethylene dichlorides and which contains in solution a mixture of zinc chloride and hydrochloric acid as catalyst each in an amount not exceeding 2% of the weight of said ester, the liquid medium employed being one which on completion of esterification yields a liquid medium which is a solvent for the mixed ester formed.

7. Process for the production of mixed esters of cellulose which comprises esterifying cellulose acetate containing free hydroxy groups in a liquid medium which comprises the anhydride of a different fatty acid containing less than six carbon atoms and an halogenated hydrocarbon selected from the group consisting of methylene and ethylene dichlorides and which contains in solution a mixture of zinc chloride and hydrochloric acid each in an amount not exceeding 0.5% of the weight of the cellulose acetate, the liquid medium employed being one which on completion of esterification yields a liquid medium which is a solvent for the mixed ester formed. 8. Process for the production of mixed esters of cellulose which comprises esterifying a carboxylic acid ester of cellulose containing free hydroxy groups in a liquid medium which comprises a carboxylic acid anhydrideand a halogenated hydrocarbon selected from the group consisting of methylene and ethylene dichlorides and which contains-in solution an acidic metal halide as catalyst in an amount not exceeding 2% of the weight of said ester, the liquid medium employed being one which on completion of the esterification yields a liquid medium which is a solvent for the mixed ester formed, mixing the finished esterification solution with hot water or a hot aqueous solution of 'a carboxylic acid of such concentration that the halogenated hydrocarbon and the mixed ester are substantially in-' amount not exceeding 2% of the weight of said ester, the liquid medium employed being one which on completion -of esterification yields a liquid medium which is a solvent for the mixed ester formed, mixing the finished esterification solution with hot water or a hot aqueous solution of a fatty acid of such concentration that the halogenated hydrocarbon and the mixed ester are substantially insoluble therein, so as to evaporate off the halogenated hydrocarbon and obtain the ester in a solid state, and separating the ester from the aqueous liquid.

HENRY DREYFUS. 

